(1) Field of the Invention
The present invention relates to a tank, to a fuel storage system, and also to an aircraft fitted with the fuel storage system. The invention relates more particularly, but not exclusively, to an aircraft, and in particular to an aircraft having a rotary wing, it being understood that a rotary wing aircraft presents specific characteristics that give rise to significant differences in comparison with an airplane or a car.
(2) Description of Related Art
A fuel storage system usually includes at least one tank containing fuel.
More precisely, a fuel storage system of an aircraft may comprise one tank group per engine of the aircraft.
Each tank group then includes a receptacle for feeding an engine. Such a receptacle is referred to as a “feeder tank”.
The feeder tank may be an independent tank or it may represent a space that always contains fuel and that is arranged within a larger tank. For example, a bell or a bag may define a feeder tank within a larger tank.
Furthermore, each tank group may include at least one tank that transmits fuel to the feeder tank of the group. Such a tank is sometimes referred to as a “main tank”.
The tank group may also have removable additional tanks referred to as “ferry tanks”.
For convenience, the main and ferry tanks are referred to together below as “storage” tanks, where the function of storage tanks is to store fuel that is to be fed to the feeder tank of the group.
Depending on the architecture, the fuel storage system of an aircraft may thus comprise at least one storage tank and a feeder tank, the feeder tank being arranged within the storage tank.
The storage system may then have transfer means between the storage tanks and the feeder tank to ensure that the feeder tank remains full, at least so long as there is a storage tank that still contains any fuel. This minimizes any risk of unpriming the pump that transfers fuel from the feeder tank to an engine.
In addition, when the aircraft contains a plurality of groups, the storage system is provided with an interconnection system between the groups. The interconnection system serves in particular to balance fuel between the groups.
The storage system usually also includes an expansion volume.
The function of such an expansion volume is to receive a fraction of the fuel stored in the tanks in the event of the fuel expanding. The expansion volume thus avoids creating high levels of tension in the walls of the tanks.
Furthermore, the storage system includes a vent system for exhausting fuel vapor to the outside of the aircraft.
A vent system is designed to prevent stored fuel overflowing while being transferred from one tank to another, or indeed whenever the aircraft presents a large inclination. The term “inclination” is used to mean an angle of the aircraft in pitching and/or in roll or even in yaw.
The vent system takes account of potential risks of siphoning under normal operating conditions.
The tanks of an aircraft and in particular of a rotary wing aircraft are sometimes arranged in the lower section of the aircraft even though the engines are arranged in the top portion of the aircraft.
A vent system then conventionally includes at least one vent line that extends upwards from each tank in order to extend outside the aircraft. At least one vent line may pass via an expansion volume.
A vent line is also provided with a first type of check valve.
Each check valve of the first type is suitable for passing both air and fuel under normal conditions. Nevertheless, beyond a threshold angle of inclination, a valve of the first type closes so as to prevent fuel from flowing through.
Under such circumstances, a valve of the first type could be referred to as a “valve for preventing overflow after rolling over”. Nevertheless, a valve of the first type is referred to below more simply and for convenience as an “anti-overflow” valve. Such a valve is sometimes also referred to as a “roll-over” valve. The anti-overflow valve thus serves to connect the tanks to the outside air, except during extreme circumstances leading to the aircraft being excessively inclined.
The vent system also includes breather lines having a second type of check valve, known as an “air-no-fuel” valve. Each air-no-fuel valve is suitable for passing a gas, such as air and/or fuel vapor, for example. In contrast, an air-no-fuel valve prevents fuel from passing independently of flying conditions and independently of the attitude of the aircraft.
Such a storage system is in widespread use.
Nevertheless, on an aircraft and in particular on a rotary wing aircraft, the tanks are arranged in a bottom portion of the aircraft. More particularly, the tanks may be arranged in the lower section of the aircraft.
In order to connect with the outside of the aircraft, the vent lines and the breather lines extend upwards from the tanks. The vent lines and the breather lines then pass through compartments of the aircraft before reaching the outside.
The vent and breather lines extend upwards from the tanks in order to avoid unwanted overflow of fuel in flight as a result of a valve malfunctioning.
If a vent or breather line opens out to the side of an aircraft, a malfunction of a valve can lead to fuel overflowing from the aircraft when performing a tight turn.
Aircraft certification regulations are strict in terms of safety and can require each vent and breather line to be made up of double-skinned pipes.
Such a double-skinned pipe comprises an internal pipe running inside an external pipe. Fuel vapor then passes along the internal pipe. A drain system may be provided between the internal and external pipes.
Vent and breather lines of that type then present manufacturing costs and weight that are not negligible.
The technological background includes document U.S. Pat. No. 6,439,506.
That document U.S. Pat. No. 6,439,506 describes a ventilation valve.
Document US 2012/0048413 describes a vent system for an airplane having a tank dedicated to system breathing.
Document WO 2010/131099 describes a fuel vapor vent valve having a dynamic pressure limiter.
Also known are the following documents: U.S. Pat. No. 2,955,787 A, U.S. Pat. No. 4,913,380 A, and WO 2005/079205 A2.